1. Field of the Invention
The present invention relates to an electronic apparatus which generates a switch signal, more particularly, though not exclusively, an imaging device which generates a switch signal using a conductive detection and common contact.
2. Description of the Related Art
A switch detection pattern of a conventionally used general tact switch will be described with reference to FIG. 9. In FIG. 9, reference numeral 91 denotes a common (GND) contact (line or pattern), and reference numeral 92 denotes a detection contact (line or pattern). Accordingly, one common contact and one detection contact make a pair to constitute a fixed contact, i.e., a switch conductive section. A movable contact of a switch operation member is operated with respect to the fixed contact to electrically interconnect the common and detection contacts, so that a conductive state is set to detect a switch operation. An end surface of the fixed contact is coated with an electrically conductive material such as a metal or carbon. An example of a tact switch is discussed in Japanese Patent Application Laid-Open No. 09-214084.
In recent single-lens reflex or digital still cameras, such tact switches are arranged in four directions, i.e., up-and-down and left-and-right directions, to constitute a direction selector used for selecting a focusing position in a finder screen or for selecting information on a monitor screen.
When the number of pieces of information to be selected are increased, selections alone in the four directions, i.e., the up-and-down and left-and-right directions, are not enough, thus creating a need to increase selectable directions. FIG. 10 illustrates a direction selector configured by annularly arranging the tact switches. Eight switches and one switch are respectively arranged in an outer periphery and in the center. The switches in the outer periphery are arranged at angular intervals of 45° around the switch in the center, and are set as switches to select angular directions and positions.
This switch needs one common contact and nine detection contacts on a circuit. In FIG. 10, nn, ne, ee, se, ss, sw, ww, nw, and cc respectively indicate detection positions of the direction selector. They are arranged in order of an upper part (north), an upper right (north east), a right (east), a lower right (south east), a lower part (south), a lower left (south west), a left (west), an upper left (north west), and a center. Reference numerals 101 to 108 denote detection contacts (lines or patterns) arranged in detection positions in the outer periphery of the direction selector. Reference numeral 109 denotes a detection contact arranged in the center. Reference numeral 100 denotes a common contact (GND) arranged in the respective detection positions to be connected together.
FIG. 11 is a sectional diagram showing a structure of the direction selector, which uses the switch detection pattern shown in FIG. 10. Reference numeral 111 denotes a direction selection member, reference numeral 112 denotes a printed circuit board, and reference numeral 113 denotes a pedestal. The printed circuit board 112 is fixed to the pedestal 113, and the direction selection member 111 is arranged on the printed circuit board 112. Reference numerals 111a, 111b, and 111c denote movable contacts, which can move up and down independently of one another with respect to a pressing operation. Reference numerals 112a, 112b, and 112c denote fixed contacts disposed on the printed circuit board 112, which can contact with the movable contacts 111a, 111b, and 111c, respectively. These fixed contacts are constructed with the conductive pattern shown in FIG. 10.
The direction selector configured as described above can be used in many compact portable electronic apparatuses because of its compact and simple structure. However, when the number of targets to be selected increases, the numbers of switches and directions increase, and the number of switch detection signals increase, thus complicating processing at a signal processing circuit. As a general method of reducing the number of signals to deal with this problem, as shown in FIG. 12, there is a conventional method of alternately thinning the number of contacts, detecting turning-on of switches at two places on both sides adjacent to the thinned place, and detecting turning-on of a switch corresponding to a middle position of the two places, i.e., the contact thinned place, by software.
Numbers and symbols in FIG. 12 are similar to those of FIG. 10. In FIG. 12, fixed contact patterns are not arranged in four places, i.e., an upper right (north east), a lower right (southeast), a lower left (southwest), and an upper left (north west). Signal detection at these omitted portions is determined by conduction of signals at the adjacent two-side positions. For example, in the case of selecting the upper right (north east), pressing is determined when conduction of both of the upper part (north) and the right (east) is detected.
Additionally, there has been proposed a technology of detecting a position and a direction more minutely by using a pointing device operable to change a resistance value of a contact in an analog fashion for a position or direction selector (a selector such as a mouse). An example of such a technology is discussed in Japanese Patent Application Laid-Open No. 2003-162946.
However, according to the aforementioned detection method, accurate direction selection may be difficult, or an erroneous operation may be induced. For example, to directly select a middle position or direction, switches at two places must be simultaneously operated. In practice, the simultaneous operation of the switches at two places is difficult. One of the switches is always operated first, and then the other switch is operated, causing a time difference or order in operation. In consequence, a problem arises in that an intended direction cannot be selected at once when the operation of the middle position is carried out.
Description will be made more specifically with reference to a finder screen illustrated in FIG. 13. Reference numerals a1 to g1 denote indicators of focusing points corresponding to the finder screen. In the case of changing an initial set position b2 of a focusing point to an adjacent focusing point c1, both upper and right switches are operated as the focusing point c1 is positioned obliquely right upward with respect to the focusing point b2.
However, as it is impossible to simultaneously operate both the upper and right switches without any time difference, the upper or right switch is detected first. When the upper switch is detected first, a detection order is from the focusing point b1 to the focusing point c1. When the right switch is detected first, as the focusing points c1 and c2 are present on the right with respect to the focusing point b2, a problem arises in that a changing position cannot be established. In consequence, with this switch configuration, a problem occurs when an oblique direction is selected.
Furthermore, when a pointing device operable to change a resistance value of a contact in an analog fashion is used, an expensive AD converter, complex in circuit processing, must be mounted. Thus, it is difficult to use such a pointing device for a compact portable electronic apparatus because of its size and cost.